private double CalculateErrorForRow(BackPropagationTrainingRow row)
{
var error = .0;
for (var i = 0; i < row.Outputs.Length; i++)
{
var d = row.Outputs[i] - _network.OutputNodes[i].Value;
error += d * d;
}
return(Math.Sqrt(error));
}
private void UpdateWeights(double adjust, double momentum, BackPropagationTrainingRow row)
{
// Compute output gradients
for (var i = 0; i < _outputGradients.Length; i++)
{
var output = _network.OutputNodes[i].Value;
var derivative = (1 - output) * output; // derivative of log-sigmoid is y * (1 - y)
_outputGradients[i] = derivative * (row.Outputs[i] - output); // gradient = (1 - O)(O) * (T-O)
}
// Compute hidden gradients
for (var i = 0; i < _hiddenGradients.Length; i++)
{
var hidden = _network.HiddenNodes[i].Value;
var derivative = (1 - hidden) * (1 + hidden); // derivative of tanh is (1 - y) * (1 + y)
var sum = .0;
for (var j = 0; j < _network.OutputNodes.Count; j++)
{
// each hidden delta is the sum of numOutput terms
sum += _outputGradients[j] * _network.OutputNodes[j].Incoming[i].Weight; // each downstream gradient * outgoing weight
}
_hiddenGradients[i] = derivative * sum; // hGrad = (1-O)(1+O) * E(oGrads*oWts)
}
// Update input to hidden weights
for (var i = 0; i < _network.InputNodes.Count; ++i)
{
for (var j = 0; j < _network.HiddenNodes.Count; ++j)
{
var delta = adjust * _hiddenGradients[j] * _network.InputNodes[i].Value; // compute the new delta = "eta * hGrad * input"
_network.HiddenNodes[j].Incoming[i].Weight += delta; // update
_network.HiddenNodes[j].Incoming[i].Weight += momentum * _network.HiddenNodes[j].Incoming[i].Delta; // add momentum using previous delta. on first pass old value will be 0.0 but that's OK.
_network.HiddenNodes[j].Incoming[i].Delta = delta; // save the delta for next time
}
}
// Update hidden biases
for (var i = 0; i < _network.HiddenNodes.Count; ++i)
{
var delta = adjust * _hiddenGradients[i];
_network.HiddenNodes[i].Bias += delta;
_network.HiddenNodes[i].Bias += momentum * _network.HiddenNodes[i].BiasDelta;
_network.HiddenNodes[i].BiasDelta = delta; // save delta
}
// Update hidden to output weights
for (var i = 0; i < _network.HiddenNodes.Count; i++)
{
for (var j = 0; j < _network.OutputNodes.Count; ++j)
{
var delta = adjust * _outputGradients[j] * _network.HiddenNodes[i].Value;
_network.OutputNodes[j].Incoming[i].Weight += delta;
_network.OutputNodes[j].Incoming[i].Weight += momentum * _network.OutputNodes[j].Incoming[i].Delta;
_network.OutputNodes[j].Incoming[i].Delta = delta;
}
}
// Update hidden to output biases
for (var i = 0; i < _network.OutputNodes.Count; i++)
{
var delta = adjust * _outputGradients[i];
_network.OutputNodes[i].Bias += delta;
_network.OutputNodes[i].Bias += momentum * _network.OutputNodes[i].BiasDelta;
_network.OutputNodes[i].BiasDelta = delta;
}
}
